The species is endemic to Spain, Portugal and France. M. splendens apparently rapidly disappears when faced with water pollution, oxygen deficiency and introduction of non-indigenous crayfish, so a regular decrease in the number of occupied sites is expected in the future. In addition, the dramatic drought from which Iberia and Southern France now suffer repeatedly will inevitably lead to a reduction of the number of populations of 30% or more in this area during the next decade. The species is assessed as Vulnerable as it is expected to show a decline of 30% in the next ten years due to a continuing decline of the habitat quality. The species should be monitored and further surveys are required to confirm the full extent of its range.

The species shows a disjunct distribution with the largest populations in southern France and northwest Iberia. Only single and old records are known from these two distribution centres. The whole area inhabited by this species reaches about 470,000 km². The two main distribution centres cover about 92,000 km² in France and 64,000 km² in northwest Spain (Galicia) and north Portugal.

The species has been reported with certainty from 14 departments in south and southwest France, but it is currently known only in 12 of these. Only in four departments it is not uncommon. In Iberia, flourishing populations are known in Galicia and north Portugal. In the rest of the western half of the Iberian Peninsula it is known from scattered and often isolated localities were it is found in low numbers. Macromia splendens is often difficult to find and is fairly rare. However, new findings (Chelmick 2006, Cordero Rivera 2000, Malkmus 2002, French INVOD inventory 2007) show that it is considerably less rare than previously believed.

It is found in streams and rivers at the slowly or nearly standing parts, even when induced by hydroelectric dams. Hydroelectric dams can support good populations when they are elongated and look like large rivers. The species is very scarcely reproducing in completely standing waterbodies.

Water pollution, drought and introduction of non-indigenous crayfish (J.-L. Dommanget pers. comm. 2008). The dramatic droughts of which Iberia now suffers repeatedly, that convert river barrage in lake-like habitats, will inevitably lead to the reduction of many populations in this area in the next decade. In addition, the introduction of exotic crayfish in the Tarn river in France led apparently to a significant decrease of the Macromia population during the last decade and this will probably continue in the future (J.-L. Dommanget pers. comm. 2008). Places where the species occurs are often favoured by tourists for swimming. A general degradation of water quality is noted almost everywhere throughout the species' range.

Necessary conservation measures include the control of water pollution and use by humans and the prevention of the introduction of non-indigenous crayfish. Establishments of nature reserves are recommended.